Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Because current treatments provide modest symptomatic relief and do not slow AD progression, a better understanding of molecular bases of AD pathology is needed. This proposal will identify and validate microRNAs (miRNAs) as a new class of drug targets. miRNAs are endogenous, short, non-coding RNAs that typically inhibit protein expression by interacting with specific recognition elements of target transcripts. AD is believed to result from overproduction of amyloid- peptide (A), derived from A precursor protein (APP), and dysregulation of proteins involved in A production (e.g. APP, -secretase/BACE1) contributes to excess A deposition. We have also recently found that miRNA can stimulate APP expression in interaction with iron homeostasis. We propose to study APP and BACE1 regulation by miRNA. We hypothesize specific miRNAs regulate endogenous levels of APP and BACE1, are dysfunctional in AD, and manipulation will reduce A. Specific Aim 1(SA1) will identify functional miRNA target sites in APP and BACE1 and validate miRNA post-transcriptional regulation of native APP and BACE1 expression. Rationale: Discover functional miRNA targets in UTRs of APP and BACE1 transcripts using. Endpoints are APP and BACE1 mRNA & proteins, and A peptides, which we predict to change with miRNA. Impact: Manipulation of miRNA regulation is a novel therapeutic approach and may be feasible for correcting gene dysregulation in AD. SA2 will test physiological interactions between miRNA validated in SA1 and their regulatory networks over APP and BACE1 expression. Rationale: Test other mechanisms of regulation likely linked to maintain homeostasis of APP, BACE1 and A. Identifying roles of miRNA in this network is vital to pharmacologically target miRNA-transcript interactions. Impact: Reveal novel mechanisms for miRNA function in AD. SA3 will assess effects of in vivo manipulation of validated miRNA in AD animal models. Rationale: Test our validated miRNAs as therapeutic targets in AD transgenic animals, including interaction with iron homeostasis, by inducing miRNA-dependent changes in translation. Impact: Validate specific miRNAs as drug targets in vivo and identify novel AD-related regulatory networks. SA4 will examine whether miRNAs implicated in regulatory control of gene products involved in A homeostasis are dysregulated in AD patients. Rationale: In SA1-3, we will identify pertinent miRNAs that modulate expression of gene products implicated in A production. If these miRNAs are also involved in AD pathology, we expect their regulation to vary in anatomical- and pathology-dependent patterns. Impact: Further demonstrate validity of miRNAs as therapeutic targets to treat AD-related dysregulation. Research dictated by our central hypothesis could cause a significant paradigm shift on the field by elucidating novel regulatory mechanisms and identifying specific miRNAs that regulate important gene products implicated in AD. Final impact will be in eventual use of these new drug targets to produce therapeutic agents to slow or halt progression in AD.